Overexpression of Bcl-2 proteins correlates with resistance to chemotherapy, clinical outcome, disease progression, overall prognosis or a combination thereof in various cancers and disorders of the immune system.
Evasion of apoptosis is a hallmark of cancer (Hanahan & Weinberg (2000) Cell 100:57-70). Cancer cells must overcome a continual bombardment by cellular stresses such as DNA damage, oncogene activation, aberrant cell cycle progression and harsh microenvironments that would cause normal cells to undergo apoptosis. One of the primary means by which cancer cells evade apoptosis is by up-regulation of anti-apoptotic proteins of the Bcl-2 family.
A particular type of neoplastic disease for which improved therapies are needed is non-Hodgkin's lymphoma (NHL). NHL is the sixth most prevalent type of new cancer in the U.S. and occurs primarily in patients 60-70 years of age. NHL is not a single disease but a family of related diseases, which are classified on the basis of several characteristics including clinical attributes and histology.
One method of classification places different histological subtypes into two major categories based on natural history of the disease, i.e., whether the disease is indolent or aggressive. In general, indolent subtypes grow slowly and are generally incurable, whereas aggressive subtypes grow rapidly and are potentially curable. Follicular lymphomas are the most common indolent subtype, and diffuse large-cell lymphomas constitute the most common aggressive subtype. The oncoprotein Bcl-2 was originally described in non-Hodgkin's B-cell lymphoma.
Treatment of follicular lymphoma typically consists of biologically-based or combination chemotherapy. Combination therapy with rituximab, cyclophosphamide, doxorubicin, vincristine and prednisone (R-CHOP) is routinely used, as is combination therapy with rituximab, cyclophosphamide, vincristine and prednisone (RCVP). Single-agent therapy with rituximab (targeting CD20, a phosphoprotein uniformly expressed on the surface of B-cells) or fludarabine is also used. Addition of rituximab to chemotherapy regimens can provide improved response rate and increased progression-free survival.
Radioimmunotherapy agents, high-dose chemotherapy and stem cell transplants can be used to treat refractory or relapsed NHL. Currently, there is not an approved treatment regimen that produces a cure, and current guidelines recommend that patients be treated in the context of a clinical trial, even in a first-line setting.
First-line treatment of patients with aggressive large B-cell lymphoma typically consists of rituximab, cyclophosphamide, doxorubicin, vincristine and prednisone (R-CHOP), or dose-adjusted etoposide, prednisone, vincristine, cyclophosphamide, doxorubicin and rituximab (DA-EPOCH-R).
Most lymphomas respond initially to any one of these therapies, but tumors typically recur and eventually become refractory. As the number of regimens patients receive increases, the more chemotherapy-resistant the disease becomes. Average response to first-line therapy is approximately 75%, 60% to second-line, 50% to third-line, and about 35-40% to fourth-line therapy. Response rates approaching 20% with a single agent in a multiple relapsed setting are considered positive and warrant further study.
Other neoplastic diseases for which improved therapies are needed include leukemias such as chronic lymphocytic leukemia (like NHL, a B-cell lymphoma) and acute lymphocyctic leukemia.
Chronic lymphoid leukemia (CLL) is the most common type of leukemia. CLL is primarily a disease of adults, more than 75% of people newly diagnosed being over the age of 50, but in rare cases it is also found in children. Combination chemotherapies are the prevalent treatment, for example fludarabine with cyclophosphamide and/or rituximab, or more complex combinations such as CHOP or R-CHOP.
Acute lymphocyctic leukemia, also known as acute lymphoblastic leukemia (ALL), is primarily a childhood disease, once with essentially zero survival but now with up to 75% survival due to combination chemotherapies similar to those mentioned above. New therapies are still needed to provide further improvement in survival rates.
Current chemotherapeutic agents elicit their antitumor response by inducing apoptosis through a variety of mechanisms. However, many tumors ultimately become resistant to these agents. Bcl-2 and Bcl-XL have been shown to confer chemotherapy resistance in short-term survival assays in vitro and, more recently, in vivo. This suggests that if improved therapies aimed at suppressing the function of Bcl-2 and Bcl-XL can be developed, such chemotherapy-resistance could be successfully overcome.
Involvement of Bcl-2 proteins in bladder cancer, brain cancer, breast cancer, bone marrow cancer, cervical cancer, CLL, colorectal cancer, esophageal cancer, hepatocellular cancer, lymphoblastic leukemia, follicular lymphoma, lymphoid malignancies of T-cell or B-cell origin, melanoma, myelogenous leukemia, myeloma, oral cancer, ovarian cancer, non-small cell lung cancer, prostate cancer, small cell lung cancer, spleen cancer and the like is described in International Patent Publication Nos. WO 2005/024636 and WO 2005/049593.
Involvement of Bcl-2 proteins in immune and autoimmune diseases is described, for example, by Puck & Zhu (2003) Current Allergy and Asthma Reports 3:378-384; Shimazaki et al. (2000) British Journal of Haematology 110(3):584-590; Rengan et al. (2000) Blood 95(4):1283-1292; and Holzelova et al. (2004) New England Journal of Medicine 351(14):1409-1418. Involvement of Bcl-2 proteins in bone marrow transplant rejection is disclosed in United States Patent Application Publication No. US 2008/0182845.
Compounds that occupy a binding site on Bcl-2 proteins are known. To be therapeutically useful by oral administration, such compounds desirably have high binding affinity, exhibiting for example Ki<1 nM, preferably <0.1 nM, more preferably <0.01 nM, to proteins of the Bcl-2 family, specifically Bcl-2, Bcl-XL and Bcl-w. It is further desirable that they be formulated in a manner that provides high systemic exposure after oral administration. A typical measure of systemic exposure after oral administration of a compound is the area under the curve (AUC) resulting from graphing plasma concentration of the compound versus time from oral administration.
Where aqueous solubility of Bcl-2 binding compounds is very low, the formulator faces a significant challenge in assuring acceptable oral bioavailability, which is strongly dependent on solubility in the aqueous medium of the gastrointestinal tract. This is true even where binding affinity is very high. The challenge becomes even greater when considering the need to provide an adequate drug loading in the formulation, so that a therapeutically effective dose can be administered in an acceptably small volume of formulated product.
Liquid dosage forms (including encapsulated liquids) can be useful for some drugs of low aqueous solubility, provided a suitable pharmaceutically acceptable solvent system (generally lipid-based) can be found that provides adequate drug loading without posing solubility or storage-stability issues. Other approaches that have been proposed for such drugs include solid dispersions, which bring their own challenges.
For a variety of reasons, such as patient compliance and unpleasant taste, a solid dosage form is often preferred over a liquid dosage form. In most instances, however, oral solid dosage forms of a drug provide lower bioavailability than oral solutions of the drug.
Various solutions to the challenge of low oral bioavailability have been proposed in the art. For example, Sharma & Joshi (2007) Asian Journal of Pharmaceutics 1(1):9-19 discuss various solubility enhancement strategies in preparing solid dispersions. A solvent evaporation method for preparing solid dispersions is described therein, mentioning as an example a solid dispersion of etoricoxib, prepared by a process that includes dissolving polyethylene glycol (PEG), polyvinylpyrrolidone (PVP or povidone) and the active ingredient in 2-propanol.
Apoptosis-inducing drugs that target Bcl-2 family proteins such as Bcl-2 and Bcl-XL are best administered according to a regimen that provides continual, for example daily, replenishment of the plasma concentration, to maintain the concentration in a therapeutically effective range. This can be achieved by daily parenteral, e.g., intravenous (i.v.) or intraperitoneal (i.p.) administration. However, daily parenteral administration is often not practical in a clinical setting, particularly for outpatients. To enhance clinical utility of an apoptosis-inducing agent, for example as a chemotherapeutic in cancer patients, a solid dosage form with acceptable oral bioavailability would be highly desirable. Such a dosage form, and a regimen for oral administration thereof, would represent an important advance in treatment of many types of cancer, including NHL, CLL and ALL, and would more readily enable combination therapies with other chemotherapeutics.